Seneca Quarry

Seneca Quarry sits along the north bank of the Potomac River with remnants of a stone cutting mill and preserved structural features scattered across the site. You can see the remains of quarrying equipment, worker areas, and facilities that were once used to extract and process red sandstone blocks.

Operations began in 1785 and supplied red sandstone for major Washington D.C. landmarks like the Smithsonian Castle and locks of the Chesapeake and Ohio Canal. The quarry closed in 1901, ending over a century of stone extraction from this site.

This site shows how early American craftsmen shaped the nation's capital through stonework and industrial skill. You can see traces of the workers' techniques in the remaining structures along the riverbank.

You can access the quarry via River Road and Riley's Lock Road, with parking near the restored quarry master's house. The riverbank location makes it easy to explore the grounds on foot while enjoying the natural setting along the water.

The sandstone extracted here displays a surprising color shift from lilac grey when freshly cut to a distinctive rust red after weathering over time. This color transformation became a recognizable feature of many buildings throughout the capital.

Location: Montgomery County

Inception: 1785

Elevation above the sea: 98 m

Address: 13201 Tschiffely Mill Rd, Poolesville, MD 20837

GPS coordinates: 39.07750,-77.35389

Latest update: December 9, 2025 18:48